Abstract
Gold bioleaching mediated by iodide oxidizing bacteria (IOB) has been proposed as a sustainable alternative to conventional technologies such as cyanidation. This study evaluated the ability of two IOB sourced from a commercial culture collection, Roseovarius (R.) tolerans DSM 11457T and R. mucosus DSM 17069T, to bioleach gold from electronic waste (e-waste) (1030 ppm gold) and sulfidic gold ore concentrate (45 ppm gold) using one-step, two-step and spent medium leaching at 1% pulp density over 10 days. Two-step bioleaching of ore concentrate resulted in the highest gold leaching yields (approximately ~100% and 34% for R. tolerans and R. mucosus, respectively), followed by spent medium leaching and one-step leaching. The yields remained low for e-waste with both strains (maximum 0.93% and 1.6% for R. tolerans and R. mucosus, respectively) and decreased over time, likely due to the instability of the solubilized gold at relatively low redox potentials (<300 mV vs. Ag/AgCl). Another limiting factor may be the partial inhibition of bacterial growth in the presence of the ore concentrate and e-waste. Therefore, future studies should evaluate the pre-treatment of the ore concentrate and e-waste to remove inhibitory and oxidant consuming compounds before bioleaching with IOB to optimize leaching yields.
Highlights
Bioleaching refers to the solubilization of target metals by microorganisms from materials such as minerals and wastes [1,2,3,4]
The elemental composition of the gold ore concentrate and e-waste were as shown in Tables 1 and 2, respectively
In one-way analyses of variance (ANOVA) for evaluating the effect of leaching method separately for each bacterial species, significant p-values were recorded for R. tolerans for day 5 and R. mucosus for days 1 and 5 (Table 4)
Summary
Bioleaching refers to the solubilization of target metals by microorganisms from materials such as minerals and wastes [1,2,3,4]. Redoxolysis, acidolysis, and complexolysis are the main mechanisms to drive bioleaching Chemolithoautotrophs such as Acidithiobacillus (A.) ferrooxidans and A. thiooxidans have been used to solubilize base metals, especially copper [6,7,8]. These species oxidize ferrous iron to ferric iron and/or reduced sulfur compounds to sulfuric acid, which leach metals from minerals and wastes via redoxolysis and acidolysis, respectively [6,9,10]. The objectives of this study were (1) to evaluate the ability of IOB, R. tolerans and R. mucosus, to bioleach gold from e-waste and sulfidic gold ore concentrate, and (2) to evaluate the effect of various leaching approaches (one-step, two-step and spent medium bioleaching) on gold extraction
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